742 



HEARING 



[CH. LIV. 



corresponds generally with the form of the osseous labyrinth, so far 

 as regards the vestibule and semicircular canals, but is separated 

 from the walls of these parts by perilymph, except where the nerves 

 enter into connection within it. The labyrinth is a closed membrane 



FIG. 544a. Right bony labyrinth, viewed 

 from the outer side. The specimen 

 here represented is prepared by sepa- 

 rating piecemeal the looser substance 

 of the petrous bone from the dense 

 walls which immediately enclose the 

 labyrinth. 1, The vestibule; 2, fen- 

 estra ovalis ; 3, superior semicircular 

 canal; 4, horizontal or external canal; 

 5, posterior canal ; *, ampullae of the 

 semicircular canals ; 5, first turn of 

 the cochlea ; 7, second turn ; 8, apex ; 

 9, fenestra rotunda. The smaller figure 

 in outline below shows the natural 



size, y (Sommering.) 



Fio. 5447). View of the interior of the left 

 labyrinth. The bony wall of the laby. 

 rinth is removed superiorly and exter- 

 nally. 1, Fovea hemielliptica ; 2, fovea 

 hemispherica ; 3, common opening of 

 the superior and posterior semicircular 

 canals ; 4, opening of the aqueduct of 

 the vestibule; 5, the superior; 6, the 

 posterior, and 7, the external semicir- 

 cular canals; 8, spiral tube of the 

 cochlea (scala tympaui); 9, opening of 

 the aqueduct of the cochlea; 10, placed 

 on the lamina spiralis in the scala ves- 



2A- 

 tibuli. y (Sommering.) 



containing endolymph, which is of much the same composition as 

 perilymph, but contains less solid matter. It is somewhat viscid, 

 as is the perilymph, and it is secreted by the epithelium lining its 

 cavity ; all the sonorous vibrations impressing the auditory nerves 

 in these parts of the internal ear, are conducted through fluid to 

 a membrane suspended in and containing fluid. In the cochlea, 

 the membranous labyrinth completes the septum between the 

 two scalce, and encloses a spiral canal, called the canalis cochleae (fig. 

 545). The fluid in the scalce of the cochlea is continuous with the 

 perilymph in the vestibule and semicircular canals. The vestibular 

 portion of the membranous labyrinth comprises two communicating 

 cavities, of which the larger and upper is named the utricle; the 

 lower, the saccule. They are lodged in depressions in the bony 

 labyrinth, termed respectively fovea hemielliptica and fovea hemi- 

 spherica. The membranous semicircular canals open into the utricle ; 

 the canal of the cochlea opens by the canalis reuniens into the 



